About twenty years ago, when I was new to Ampico "B" systems, I
complained to Dr. Hickman by phone that the "B" block valves repeated
perfectly at their elbows, but not at the tracker bar.  He said, "Well,
we only tested them for repetition at the bench, and so there must have
been a defect in the valve which only became evident when long lengths
of tubing were added."

I found this peculiar, and of course, it was not true.  I continued to
experiment, and found that if the pouches were tight enough to hold a
modicum of suction, yet still flexible, they repeated perfectly down to
2" of water vacuum!  I never had occasion to report this to Dr. Hickman
until years later, when he told me in person that the valves were
defective when used with long tubing (forgetting that he got the false
information from me, years before!)  I assured him that the valves were
perfect under all conditions, when working as intended.

I agree with Craig Brougher on most of his points, adding that there is
a potential for problems if the tiny channel from the pouch to the ball
bleed is not airtight, or filled with glue during reassembly, etc.

However, under a strong light, I have no trouble finding the joint in
these blocks through the original orange shellac, to separate them.  It
is best to drive single-edged razor blades into the joint from the back
after removing the gasket, resting it against the (accessible from that
side) pouch block surface, and working it around to the front.
Sometimes a piece will splinter a bit (just glue it back, or fill it
with sawdust mixed with hot glue), but usually there is a clean break.

Having little experience as yet with Craig's preferred sealant
Permaseal, I use home-made shellac (mixed from flakes) , which is 100%
airtight although it becomes less so with a few decades, to reseal the
blocks.  Since it re-melts the original shellac, there is no need to
sand it off.  The blocks also look authentic, exactly as they did when
they were new, which is always nice.  In my opinion this is a
satisfactory restoration technique, since by the time it leaks, other
things will need renewal as well anyway, and it only takes a few hours
to put another coat of shellac on the valves, in twenty years or so.

In any case, unless these blocks are sealed on the outside, there is a
direct leak into the static stack suction, so it must be done.  I find
that the valve travel, if set by measurement, should be about 3/64,"
and definitely not less.

One thing I find curious, is that the .008" thickness of the pouches
cannot be seen at the seam in factory unopened blocks.  The seam is
completely closed around the pouch, it appears!  I have often wondered
if these were glued under tremendous pressure, prior to cutting the
blocks apart.  When I re-glue them with hot glue, regardless of the
pressure used, the .008" thickness of the pouch (while well sealed at
the edge) can be clearly seen!  So I usually don't use a great deal of
pressure.  Hot glue is an adequate filler to take up the tiny voids
between the pouch and the surrounding wood.

Larry Broadmoore
Broadmoore Piano Company
Phone: (818) 365-6231  Fax:   (818) 361-0911